PROJECT SUMMARY/ABSTRACT We propose to support the established Prostate cancer Active Surveillance Study (PASS) cohort, which is a large multi-institutional cohort of men with clinically localized prostate cancer who have elected active surveillance to manage their cancer. With broad eligibility criteria designed to represent the population of men who utilize active surveillance, the cohort has over 2,100 participants with extensive clinical and epidemiological data (demographic, lifestyle, quality of life, long-term outcomes) and longitudinal biospecimens (germline DNA, serum, plasma, urine, and prostate tissue) collected according to a standardized protocol. The cohort was established in 2008 in response to the growing evidence of prostate cancer overtreatment and the need for a prospective study to discover and validate biomarkers of prostate cancer progression, and to identify determinants of cancer progression and patient outcomes. Over the past decade, the cohort has amassed a wealth of data and biospecimens so that it serves as the foundation for addressing critical questions relevant to the optimal personalized management of early stage prostate cancer. The successful funding of this application will support a robust infrastructure for PASS that in turn will ensure the availability of PASS data and specimens to facilitate research addressing determinants of cancer progression, recurrence, and outcomes. A substantial proportion of these research endeavors are encompassed in currently funded federal grants, and the successful completion of the current and future projects relies on the continued success of the PASS enterprise. The impact of this cohort lies in its potential to investigate research questions of paramount importance: to identify better prognostic markers of prostate cancer aggressiveness; to understand the clinical management, progression and outcomes of early stage prostate cancer; to tailor the approach of active surveillance based on individual characteristics and preferences; to characterize associations between clinicopathologic factors, patient lifestyle, and disease biology; to develop new tools to communicate medical information to patients; and to understand decision- making among patients on active surveillance, in particular with regards to quality of life, anxiety, and regret . The successful completion of these transformative research endeavors will address unmet needs in the most commonly diagnosed male cancer and substantially reduce the current public health burden of early stage prostate cancer.